Kimia SMA - Stokiometri (1) - Massa Atom Relatif, Massa Molekul Relatif, Ar, Mr (D)

Summary

In this educational video, the instructor explains fundamental topics in stoichiometry, including relative atomic mass and molecular mass. The video begins with a discussion on atomic mass relative to carbon-12, followed by practical examples and calculations. The instructor then covers molecular mass, demonstrating how to calculate the molecular mass of compounds like CH3COOH and X2SO4. The lesson concludes with an explanation of isotopes, their average atomic mass, and how to calculate isotope abundances, using examples like zinc and chlorine. Viewers are encouraged to practice these concepts for better understanding.

Takeaways

• 😀 Atomic mass is the comparison of the average mass of an atom or element to 1/12 of the mass of a carbon-12 atom.
• 😀 To calculate relative atomic mass (Ar), use the formula: Ar = mass of element / (1/12 * mass of carbon-12).
• 😀 The example provided demonstrates how to calculate Ar using a mass of 4.037 × 10^-23 g for element X and carbon-12 mass of 1.99 × 10^-23 g.
• 😀 Molecular mass (Mr) is the comparison of the average mass of a molecule to 1/12 of the mass of a carbon-12 atom.
• 😀 To calculate Mr, sum the Ar values of all atoms in a molecule. For example, the Mr of CH3COOH is calculated as 60.
• 😀 The molecular mass of compounds like X2SO4 and their corresponding isotopic values can be calculated using the same method.
• 😀 Isotopes are elements that have the same atomic number but different mass numbers. Examples include Zn-65 and Zn-66.
• 😀 The relative atomic mass of an element can be found by averaging the masses of its isotopes based on their relative abundances.
• 😀 In the example of zinc, the relative atomic mass is calculated using the formula for isotope abundance: 60% Zn-65 and 40% Zn-66, yielding a value of 65.66.
• 😀 When dealing with isotopes of elements like chlorine (Cl-35 and Cl-37), their relative abundances can be determined through equations based on their average atomic mass, which in this case is 35.5.
• 😀 Chlorine isotopic abundances can be solved algebraically, where the percentage of Cl-35 is found to be 75%, and Cl-37 is 25%.

Q & A

What is the definition of relative atomic mass?

Relative atomic mass is the comparison of the average mass of an atom of an element to 1/12th of the mass of a carbon-12 atom.

How is the relative atomic mass of an element calculated?

The relative atomic mass (Ar) of an element can be calculated using the formula: Ar = (mass of the element) / (1/12 of the mass of a carbon-12 atom).

What is the relative atomic mass of element X if the mass of one atom of X is 4.037 × 10^-23 g and the mass of a carbon-12 atom is 1.99268 × 10^-23 g?

The relative atomic mass of element X is 24.27, calculated using the formula Ar = (4.037 × 10^-23) / (1/12 × 1.99268 × 10^-23).

How do you calculate the mass of 10 atoms of an element if the mass of one atom is known?

To calculate the mass of 10 atoms, multiply the mass of a single atom by 10. For example, if the mass of one atom is 9.3 × 10^-23 g, the mass of 10 atoms would be 9.3 × 10^-22 g.

What is the difference between relative atomic mass and relative molecular mass?

Relative atomic mass refers to the mass of a single atom compared to a carbon-12 atom, while relative molecular mass (Mr) refers to the mass of a molecule relative to the mass of a carbon-12 atom. Mr is the sum of the relative atomic masses of the atoms in the molecule.

How do you calculate the relative molecular mass (Mr) of CH3COOH (acetic acid)?

The relative molecular mass of CH3COOH is calculated by adding the relative atomic masses of its elements: 2 × 12 (for C) + 4 × 1 (for H) + 2 × 16 (for O), resulting in 60.

What is the method for calculating the molecular mass of a compound containing multiple elements?

To calculate the molecular mass of a compound, sum the relative atomic masses of all the atoms in the molecule, considering the number of atoms of each element in the molecular formula.

How is the average atomic mass of an element with isotopes calculated?

The average atomic mass of an element with isotopes is calculated by taking the sum of the percentage abundance of each isotope multiplied by its atomic mass.

What is the average atomic mass of zinc (Zn) given 60% of Zn-65 and 40% of Zn-66?

The average atomic mass of zinc is 65.66, calculated by: (60% × 65) + (40% × 66).

How do you determine the isotopic abundance of chlorine isotopes if the atomic mass is known?

To determine the isotopic abundance of chlorine isotopes, use the equation: (percent abundance of Cl-35 × 35) + (percent abundance of Cl-37 × 37) = the average atomic mass. If the average mass is 35.5, the isotopic abundances are 75% for Cl-35 and 25% for Cl-37.